ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Antideo Email Validator - Antideo Email Validation plugin for WordPress ensures that you get to validate emails in real time
clearout.io - Clearout Email Finder & Email Verification Service - Drive sustainable business growth by expanding your reach, lowering hard bounces, and improving deliverability rates.
CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Sender Policy Framework - This is a diagnostic tool that acts as a Sender Policy Framework (SPF) record lookup